The concentration of nitrogen oxide (NOx) emissions in the exhaust gas produced by the combustion of fuel in gas turbine combustion system has been a longstanding concern in the field. Currently, the emission level requirement is less than 25 ppm of NOx for an industrial gas exhaust. Nitrogen oxides (NOx) include various nitrogen compounds such as nitrogen dioxide (NO2) and nitric oxide (NO). These compounds play a key role in the formation of harmful particulate matter, smog (ground-level ozone), and acid rain. Further, these compounds contribute to eutrophication (the buildup of nutrients in coastal estuaries) that in turn leads to oxygen depletion, which degrades water quality and harms marine life. NOx emissions also contribute to haze air pollution in our national parks and wilderness areas. As a result, gas turbine combustion systems having low NOx emissions are of utmost importance.
The primary method for reducing NOx emissions in gas combustion systems is to reduce the combustion reaction temperature by reducing the flame temperature. For example, as discussed in U.S. Pat. No. 6,418,725, one conventional method for reducing NOx emissions to inject steam or water into the high-temperature combustion area to reduce the flame temperature during the combustion. The deficiencies of this method include the requirement for a large amount of water or steam and reduced combustor lifetime due to increased combustor vibrations resulting from the injection of water. Moreover, reducing the flame temperature results in a significant drop in efficiency of the combustion system as it is well-known that lowering the flame temperature substantially reduces combustion efficiency. Accordingly, combustion systems that are able to maintain a relatively high flame temperature for combustion efficiency and are able to maintain low NOx emissions are desired.